Magnetic fields in star-forming regions - The potential of polarimetric observations
Magnetic fields are expected to have a significant influence on the formation and evolution of stars and planets. In order to investigate the influence of the magnetic field, two different measurement methods are usually used. Firstly, the observation of the polarized continuum radiation, provided that this is caused by aligned non-spherical dust grains, and secondly, the observation of Zeeman split spectral lines. Many important questions arise with regard to these polarimetric observations, whereby two of them related to the Zeeman splitting will be answered in this talk. The first study investigates the uncertainty of the Zeeman analysis, which is usually used to estimate the magnetic field strength in the line-of-sight direction from spectral line observations of molecular clouds. Based on radiative transfer simulations of the OH spectral line at ν = 1665 MHz, the uncertainty of the Zeeman analysis in previous observations of molecular clouds is sufficiently low. Furthermore, approximations were derived to estimate the uncertainty of the Zeeman analysis for other spectral lines of various species as well. The second study investigates which constraints for magnetic fields in circumstellar disks can be obtained from Zeeman observations of the ν = 113 GHz CN lines. Based on radiative transfer simulations of these spectral lines, the strength and structure of the magnetic field of circumstellar disks can be estimated using spatially resolved Zeeman observations. However, with the capabilities of recent and upcoming instruments and observatories even spatially unresolved observations would be challenging. Nevertheless, it is also possible to obtain important information about the magnetic field of circumstellar disks from spatially unresolved Zeeman observations. Furthermore, the magnetic field strength significantly increases the success of such observations, whereas the number of CN molecules and the inclination of the disk only have a minor influence.